Question

Tarnish on copper is the compound CuO. A tarnished copper plate is placed in an aluminum pan of boiling water. When enough salt is added so that the solution conducts electricity, the tarnish disappears. Imagine that the two halves of this redox reaction were separated and connected with a wire and a salt bridge.
Calculate the standard cell potential given the following standard reduction potentials:

Al3++3e-?Al; E?=?1.66 V
Cu2++2e-?Cu; E?=0.340 V

Answer 1

Answer:  2.00 V

Explanation:

The balanced redox reaction is:

$2Al+3Cu^{2+}\rightarrow 2Al^{3+}+3Cu$

Here Al undergoes oxidation by loss of electrons, thus act as anode. Copper undergoes reduction by gain of electrons and thus act as cathode.

$E^0=E^0_{cathode}- E^0_{anode}$

Where both $E^0$ are standard reduction potentials.

$Al^{3+}+3e^-\rightarrow Al$ $E^0_{[Al^{3+}/Al]}=-1.66V$

$Cu^{2+}+2e^-\rightarrow Cu$ $E^0_{[Cu^{2+}/Cu]}=0.340V$

$E^0=E^0_{[Cu^{2+}/Cu]}- E^0_{[Al^{3+}/Al]}$

$E^0=+0.34- (-1.66V)=2.00V$

Thus the standard cell potential is 2.00 V